This editorial is from the June issue of M&A’s Arizona Water Policy Update.
Although the Upper and Lower Colorado River Basin states strive to cooperate on water management, sometimes natural events cause misfortune in one basin but benefit the other. In the next few weeks, the record high snowpack is anticipated to melt and cause flooding in Wyoming and Colorado before filling the reservoirs that supply water to Arizona, Nevada, and California.
Mountain snowpack is currently at record highs in parts of the Upper Basin. Locally, snow is up to 5 to 10 times deeper than normal for this time of year; basinwide for the Upper Colorado River headwaters, the snow-water equivalent is currently 285 percent of normal and 258 percent of normal for the Upper Basin as a whole. Snowmelt runoff is expected to shatter streamflow records in many parts of the western slope, causing major concerns about flooding if warm weather persists and leads to rapid melting of the snowpack. As of June 1, Colorado River tributaries in the Upper Basin are flowing at levels between 200 percent and 300 percent of average and are quickly approaching flood stage, with plenty of snow left to melt. Northern Water District’s minimum estimates still represent all-time high flows for many reaches of the Colorado River headwaters. And it is not out of the question for snow to continue to accumulate in certain portions of the Upper Basin. Reclamation projects that inflows to Flaming Gorge Reservoir may reach or exceed the record inflows of 1983 and 1984.
In addition to uncertainties about the timing and rate of snowmelt in the Upper Basin, Reclamation engineers stress that their projections for “unregulated inflow” into Lake Powell are also highly uncertain. Currently, the median volume forecasted for 2011 is 15.34 MAF (127 percent of average). Given the available data, Reclamation estimates with 80 percent certainty that inflow will be between 12.4 MAF (103 percent of average) and 18.1 MAF (150 percent of average).
Regardless of the timing and precise magnitude, inflows to Lake Powell will be historic this year. Only in 8 of the 47 years of Lake Powell’s existence have inflows exceeded the projected range. Although water managers are unlikely to announce the end of the current drought, the floods in the Upper Basin are expected to suspend talk of the Lower Basin hitting its first shortage level for at least another 5 years, which should bode well for relative peace between the basins on this issue.